Carrying a backpack is a convenient method to travel with gear. For many people it is a preferred way to travel into the wilderness to experience the beauty of nature. While traveling this way, it is usually desirable to carry water to drink. This water can be carried in water bottles, or in personal hydration systems. A personal hydration system consists of a water reservoir and a hose that leads to a mouthpiece that is used by a person to obtain a drink.
When traveling in areas where pure water is not available, there are two popular choices to obtain pure water. The first is to chemically treat the water. The second method is to filter the water. Portable water filter systems for backpackers are currently available with pumps associated with them. Producing pure water with these pumps requires pumping dirty water through the filter and into a drinking water bottle or personal hydration system. The disadvantage of pumping is that it requires manual effort and time. Chemically treating water has other disadvantages, including managing the treatment chemicals, needing to wait a period of time for the chemical treatment to become effective, and tasting and ingesting the treatment chemicals.
Convenience is an important factor when traveling with a backpack. Needing to take off a backpack to access important items slows down a traveler, and in a subtle way actually reduces the safety of the backpacker. When an item is difficult to access, the user will naturally access that item less frequently. The result of this is that the backpacker will use a part of his safety margin by delaying his use of the item in question. When snacks are difficult to access, the backpacker will wait longer before he eats. When a map is difficult to get to, the backpacker will refer to it less. When rain gear is difficult to reach, the backpacker will hike longer in drizzle before deciding to put on his rain gear. The drinking tube of a personal hydration system makes accessing water in a backpack easy and convenient. It is important that other items in a backpack also be easy and convenient to access as well. These items frequently include sunscreen, snacks, maps, a compass, insect repellant, a hat and rain gear.
Being able to comfortably carry a varying load is also an important feature of a good backpack. At the start of a week long camping trip, a typical backpacker might carry eleven pounds of food, and this food adds to the weight and volume carried in the backpack. Over the course of that camping trip, the food and its associated weight and volume disappear. A good backpack needs to be easy to carry and conform to the body of the person carrying it, and it needs to retain its properties of comfort and function while carrying loads that differ in volume and weight. Backpacks commonly use rigid frames to stabilize the geometry of the shoulder straps and the waist belts. Frames allow a pack to carry full or partially empty loads, while maintaining unchanging geometries of shoulder straps and waist belts. Backpacks also commonly use horizontal straps and lacing to allow the backpack to shrink its volume.
Backpack frames are also important because they provide a rigid structure that allows the weight of the backpack to be shared between the shoulder straps and the waist belts. When the weight is carried on the shoulder straps, the body of the pack is suspended from the attachment areas of the shoulder straps to the pack, typically near the top of the pack. When the weight of the pack is carried by the waist belt, the body of the pack is lifted from the attachment area of the waist belt to the pack, typically near the bottom of the pack. A rigid, or nearly rigid, connection between the shoulder straps and the waist belts is essential to allow the shoulder straps and waist belts to share the load of the backpack.